There are actually two buttons which are “UNETE” AND “MI CUENTA” in the top header and they both have font-awesome icons.

If you want, you can use this url of a possible png icon, for the two buttons and I see how the icon would look on the buttons:
https://tuwebtop.com/eunicegarciaruiz6/wp-content/uploads/2021/01/flecha-doble-volver-blanca.png

Thank you very much dear Elise